I'm kind of with Del where I feel the games are both a mixed bag. I'll second the fact the Collector's never really felt like a good antagonist and I'll agree that I still think it was kind of dumb being the third game in and we're still trying to introduce new characters and make you feel as invested in them as you did with the characters you've been with since the first game. I feel both games still suffer from feeling way too scripted in the gameplay department, but I'll give ME3 points for better level design and enemy variety.

In fact, I feel ME3 was a better game overall in terms of actual gameplay. They brought back better customization which was still nowhere near as good as ME1's but much appreciated after ME2 mostly gutted it. Better enemy varieties with honest to goodness enemies that would receive Kill on Sight orders from me, and the environments went back to a more organic structure where boxes and convenient waist high walls are not placed in rooms in convenient trench warfare fashion. The Biotics Academy area especially stood out to me.

Story side of things is a bit weird for me. I feel like both ME2 and ME3 basically took one side of what ME1 did right at the cost of ignoring the other. ME2 was very character driven since the core plot was building your elite unit, but it lacked a compelling main plot because the Collectors weren't nearly as menacing as the Reapers and the game lacked a major foil like Saren to keep you focused. ME3 is way more plot relevant and barring some few really good conclusions to character arcs established in the earlier games, most of the character interaction involved the three new party members and just a "where are they now" attitude with the rest. The fact both games had a bad habit of sidelining my favorite characters from the previous games never set well with me, and I am still absolutely pissed off about the fact that my two fave characters can't both survive the series. Though I will say that Liara really grew on me over the course of the series. She was one of my favorite party members by ME3 despite being one of my least favorite characters in the first game. Despite the main ending kind of being meh, I was really more invested in the Geth/Quarian and Krogan issues, so them being front and center in the plot of ME3 was nice instead of being relegated to optional side stuff in ME2. There is definitely some good and bad in both games in this department.

Overall, the sequels just never really recaptured the magic of the first game for me. ME1 was like playing something like Star Trek or Babylon 5, whereas the sequels kind of felt like more a Hollywood blockbuster that lost the sense of exploring a really cool alien political setting for me. The first game just set-up a really deep narrative of galactic empires and man trying to find it's place in all of it, and the sequels basically Avatared it with humanity taking center stage to magically right centuries of political conflict, when it wasn't just blatantly ignored except to add drama for a one and done side mission or two.